An air conditioning unit for an operator's compartment of a work vehicle has a door for switching between internal air and external air, a fan, an evaporator, a heater core, etc. The fan introduces internal air and external air into the air conditioning unit and sends the air to the evaporator and the heater core, and then delivers the air to an internal space of the operator's compartment. This conditions the air in the internal space of the operator's compartment. Such an air conditioning unit is disclosed in Japanese Patent Laying-Open No. 2013-126876 (PTD 1), for example.